Univalued Binary Tree Python Solution

lcpy gen -n 965   # by problem number
lcpy gen -s univalued_binary_tree   # by problem name

Input: root = [1,1,1,1,1,null,1]
Output: true

Input: root = [2,2,2,5,2]
Output: false

from leetcode_py import TreeNode


class Solution:
    # Time: O(n)
    # Space: O(h)
    def is_unival_tree(self, root: TreeNode[int] | None) -> bool:
        if root is None:
            return True
        stack = [root]
        target = root.val
        while stack:
            node = stack.pop()
            if node.val != target:
                return False
            if node.left is not None:
                stack.append(node.left)
            if node.right is not None:
                stack.append(node.right)
        return True